Typically, the conventional ball-point pens have oily inks filled therein. However, some novel types of ball-point pens containing aqueous inks instead of the oily inks have recently developed, wherein the aqueous inks are less viscous than the oily inks. The flow rate of the aqueous inks effluent from such novel type ball-point pens is high enough to ensure the drawing of thicker lines, but these pens are likely to cause the problem of "scratchy lines or blurred strokes".
This problem results from the fact that a ball-retaining cavity in each of those novel type ball-point pens can not necessarily hold therein a sufficient amount of an aqueous ink less viscous than the oily inks. If the novel type ball-point pens are left for a while to take their upside down position where penpoint tips face upwards, then a considerable amount of the ink will flow down into an ink reservoir from the ball-retaining cavity. Therefore, the ball-retaining cavity will become almost empty to render scratchy or blurred the first strokes or lines.
Some improvements proposed to incorporate check valves to resolve the problem of such a backflow of the ink are disclosed in:
Japanese Patent Publication No. Sho. 28-717, PA1 Japanese Utility Model Publication No. Sho. 54-15703, ibid. 54-15704, PA1 Japanese Utility Model Laying-Open Gazette No. Sho. 62-30684, PA1 Japanese Utility Model Publication No. Hei. 4-52067, PA1 Japanese Utility Model Laying-Open Gazette No. Hei. 6-64956, and ibid. 6-83376.
The Japanese Utility Model Publication No. Hei. 4-52067 is regarded as the most typical one, and the structure of ball-point pen disclosed therein will be discussed below.
FIGS. 25(a) and 25(b) are cross-sectional views of the ball-point pen shown in this publication and comprising a built-in valve.
A ball-point pen 100 shown in the publication 4-52067 comprises a pen-handle 101 and an ink core 102 inserted therein. The ink core 102 consists of a penpoint tip (a.k.a. `nib`) 105, an ink reservoir 106, a connector 107 and a valve body 108. The penpoint tip 105 has a writing ball 109 installed therein. The ink reservoir 106 is a cylindrical member to hold therein an aqueous ink. The connector 107 connects the penpoint tip 105 to the ink reservoir 106 and has a bore 110 communicating therewith. A valve seat 111 and lugs 113 are formed in and integral with the bore 110.
The penpoint tip 105 is fitted in a distal end of the connector 107, with the ink reservoir 106 being fitted thereon.
The prior art ball-point pen 100 has a valve chamber 115 defined between the valve seat 111 and the lugs 113, within the bore 110 of the connector 107.
If and when this prior art pen 100 takes a position where its penpoint tip 105 faces upwards, then the valve body 108 will contact and rest on the valve seat 111 in a manner shown in FIG. 25(a). Consequently, a central opening through the valve seat 111 will be stopped so as to prevent the ink in the penpoint tip 105 from flowing backward therefrom.
However, the penpoint tip 105 may be positioned to face down-wards so that the valve body 108 leaves the seat 111, then engages with and stands still on the lugs 113 as shown in FIG. 25(b). The ink in the reservoir 106 will thus move towards the penpoint tip 105, flowing through gaps that exist between the valve body 108 and the lugs 113.
In the prior art ball-point pen 100, its spherical valve body 108 is movable fore and aft within the valve chamber 115, in response to whether the pen stands upright or whether reversed upside down. Thus the ink is permitted to flow forward towards the penpoint tip 105, but is inhibited from flowing backward towards the ink reservoir 106. This structure will diminish the problem of "scratchy first strokes".
In the pen 100 known in the art, an inner periphery of the bore 110 extending through the connector 107 serves as a peripheral wall of the valve chamber 115. Unfavorably, it is difficult for the valve chamber 115 thus formed to be of a sufficient preciseness.
In detail, the connector 107 may usually be formed by the injection molding such that the lugs 113 protruding from its inner periphery renders `undercut` a region where the valve chamber 115 is located. Therefore, a wrenching force will unavoidably be applied to such a region of the valve chamber 115 when removing those connectors from an injection mold, thus failing to provide them with an unvarying accuracy in dimension and thereby lowering the highest possible precision.
It also is difficult to design and adopt an optimum clearance between the valve chamber 115 and the valve body 108 in such a prior art ball-point pen 100. If the clearance is too small, then the valve body 108 moving within said chamber will sometimes be stopped therein at an intermediate position. In a case wherein the clearance is too large, the valve body 108 will possibly rock transversely and undesirably fail to rest tightly on the valve seat 111.
The other prior art ball-point pens likewise suffer from the same or similar problems. In each of the ball-point pens known from the Publications or Gazettes listed above, an internal surface of the connector is utilized as the periphery of the valve chamber. This will result in a lower dimensional accuracy of the valve chambers thus formed. Accordingly, there will be involved a difficulty in predetermination of an appropriate clearance between each valve chamber and the valve body, thus failing to ensure smooth motion of the valve body.
In view of the problems inherent in the prior art, a primary object of the present invention is to provide a ball-point pen such that its valve chamber is formed with an epoch-making accuracy in dimension and such an improved accuracy will in turn enable optimization of the clearance between a valve body and the valve chamber, whereby the valve body thus rendered capable of moving more smoothly will afford a smoother hand-writing.